1. Technical Field
The present invention relates to a heat exchanger, and more particularly, to a heat exchanging condenser for use in an automotive air-conditioning system.
2. Description of the Prior Art
With reference to FIG. 1, a conventional refrigerant circuit for use, for example, in an automotive air-conditioning system is shown. Circuit 1 includes compressor 10, heat exchanger 20, receiver or accumulator 30, expansion device 40, and evaporator 50 serially connected through pipe members 60 which link the outlet of one component with the inlet of a successive component. The outlet of evaporator 50 is linked to the inlet of compressor 10 through pipe member 60 so as to complete the circuit. The links of pipe members 60 to each component of circuit 1 are made such that the circuit is hermetically sealed.
In operation of circuit 1, refrigerant gas is drawn from the outlet of evaporator 50 and flows through the inlet of compressor 10, and is compressed and discharged to heat exchanger 20. The compressed refrigerant gas in heat exchanger 20 radiates heat to an external fluid flowing through heat exchanger 20, for example, atmosphere air, and condenses to the liquid state. The liquid refrigerant flows to receiver 30 and is accumulated therein. The refrigerant in receiver 30 flows to expansion device 40, for example, a thermostatic expansion valve, where the pressure of the liquid refrigerant is reduced. The reduced pressure liquid refrigerant flows through evaporator 50, and is vaporized by absorbing heat from a fluid flowing through the evaporator, for example, atmospheric air. The gaseous refrigerant then flows from evaporator 50 back to the inlet of compressor 10 for further compression and recirculation through circuit 1.
With further reference to FIGS. 1a, and 2-5, a prior art embodiment of heat exchanger 20 as disclosed in Japanese Patent Application Publication No. 63-112065 is shown. Heat exchanger 20 includes a plurality of adjacent, essentially flat tubes 21 having an oval cross-section and open ends which allow refrigerant fluid to flow therethrough. A plurality of corrugated fin units 22 are disposed between adjacent tubes 21. Circular header pipes 23 and 24 are disposed perpendicularly to flat tubes 21 and may have, for example, a clad construction. Each header pipe 23 and 24 includes outer tube 26 which may be made from aluminum and inner tube 28 made of a metal material which is brazed to the inner surface of outer tube 26. Outer tube 26 has slits 27 disposed therethrough. Flat tubes 21 are fixedly connected to header pipes 23 and 24 and are disposed in slits 27 such that the open ends of flat tubes 21 communicate with the hollow interior of header pipes 23 and 24. Inner tube 28 includes portions 28a which define openings corresponding to slits 27. Portions 28a are braced to the inner ends of flat tubes 21 and ensure that tubes 21 are hermetically sealed within header pipes 23 and 24 when inserted in slits 27.
Header pipe 23 has an open top end and a closed bottom end. The open top end is sealed by inlet union joint 23a which is fixedly and hermetically connected thereto. Inlet union joint 23a is linked to the outlet of compressor 10. Partition wall 23b is fixedly disposed within first header pipe 23 at a location about midway along its length and divides header pipe 23 into upper cavity 231 and lower cavity 232 which is isolated from upper cavity 231. Second header pipe 24 has a closed top end and an open bottom end. The open bottom end is sealed by outlet union joint 24a fixedly and hermetically connected thereto. Outlet union joint 24a is linked to the inlet of receiver 30. Partition wall 24b is fixedly disposed within second header pipe 24 at a location approximately one-third of the way along the length of second header pipe 24 and divides second header pipe 24 into upper cavity 241 and lower cavity 242 which is located from upper cavity 241. The location of partition wall 24b is lower than the location of partition wall 23a.
In operation, compressed refrigerant gas from compressor 10 flows into upper cavity 231 of first header pipe 23 through inlet union joint 23a, and is distributed such that a portion of the gas flows through each of flat tubes 21 which are disposed above the location of partition wall 23b, and into an upper portion of upper cavity 241. Thereafter, the refrigerant in the upper portion of cavity 241 flows downward into a lower portion of upper cavity 241, and is distributed such that a portion flows through each of the plurality of flat tubes 21 disposed below the location of partition wall 23b and above the location of partition wall 24b, and into an upper portion of lower cavity 232 of first header pipe 23. The refrigerant in an upper portion of lower cavity 232 flows downwardly into a lower portion, and is again distributed such that a portion flows through each of the plurality of flat tubes 21 disposed below the location of partition wall 24b, and into lower cavity 242 of second header pipe 24. As the refrigerant gas sequentially flows through flat tubes 21, heat from the refrigerant gas is exchanged with the atmospheric air flowing through corrugated fin units 22 in the direction of arrow W as shown in FIG. 5. Since the refrigerant gas radiates heat to the outside air, it condenses to the liquid state as it travels through tubes 21. The condensed liquid refrigerant in cavity 242 flows out therefrom through outlet union joint 24a and into receiver 30 and the further elements of the circuit as discussed above.
With reference to FIG. 6, a conventional heat exchanger which is disclosed in U.S. Pat. No. 4,615,385, issued in the name of Saperstein et al., is shown. Heat exchanger 130 includes first and second header pipes 100 which have a plurality of slots 200. These slots are for the insertion of ends of flat tubes 300 as explained with regard to FIG. 2 above. Dome-shaped portions 220 are positioned between the respective slots 200 formed through header pipes 100.
Since the pressure difference between the fluid and the atmosphere can be great, the area adjacent the slots must be strengthened to increase the pull out resistance of the tubes 300. Dome-shaped portions 220 are designed to improve the pull out resistance force of header pipe 100 to prevent the deformation of the header pipe caused by high pressure fluid in the header pipes 100.
However, if there is a dome-shaped portion between respective slots 200 on header pipe 100 as shown in FIG. 7, channels 210 are defined between the outer surfaces of flat tubes 300 and dome-shaped portions 220. Channels 210 create dead spaces so that air passing therethrough does not perform a heat exchange function because corrugated fin units 400 are not disposed in the space of channels 210. In addition, since condensed water can be more easily accumulated at channels 210 as compared with the other portions of the heat exchanger, an oxygen concentration cell may be formed, and corrosion may occur on header pipes 100.
Other problems of conventional heat exchangers are described below. Dome-shaped portions 220 are formed on header pipe 100 which is generally made of clad materials. These clad materials can be a layer or layers of brazing materials coated on the outer surface of an aluminum core. In heat exchanger 130 with header pipes 100 using the above clad materials, if the top end surfaces of dome-shaped portions 220 contact the end of corrugated fin unit 400, which is also made of aluminum, while being heated in a furnace, fin units 400 will become brazed to dome-shaped portions 220. As shown in FIG. 8, which shows the heat exchanger 130 before heating, contact between the dome-shaped portions 220 and corrugated fin units is slight. After heating, the longitudinal length of corrugated fin units 400 is expanded, thus deforming the ends of the units as shown in FIG. 9. The same process occurs for all fin unit ends thus decreasing the strength of all corrugated fin units.
The process of brazing fin units 400 to the outer surface of header pipes 100 occurs as follows. Brazing material 100b which is on the outer surface of header pipes 100 adheres to corrugated fin units 400 that are in contact with header pipes 100. Silicon contained in brazing material 100b is diffused into corrugated fin units 400. The melting point of corrugated fin unit 400 is dependent upon the silicon content and the atmospheric temperature in the furnace, therefore, the more silicon that diffuses into corrugated fin unit 400 the lower the melting point. Upon sufficient silicon diffusing into corrugated fin units 400, the ends of the fins units melt as shown in FIG. 9. The resultant channel or dead space 210 causes a problem in that inefficient heat transfer results. Accordingly, in order to avoid this problem it is necessary to assemble the heat exchanger such that there is no contact between header pipes 100 and corrugated fin units 400. This can be accomplished by inserting spacers between dome-shaped portions 220 and corrugated fin units 400; however, this is an expensive and time consuming solution to the problem.
Another solution to the problem of creating channels 210 is to weld header pipes 100 to flat tubes 300. This solution is extremely expensive and labor intensive. Heat exchangers made by this method are prohibitively expensive.